1. Field of the Invention
The present invention relates to compositions for supporting pastes, their preparation and use in the field of dental technology.
2. Description of the Related Art
Sintering or crystallization of glassy or glass ceramic molded parts is carried out at high temperatures, sometimes close to the softening or even melting point of these materials. In order to avoid warpage of the molded parts, it is necessary to support these parts.
It is known from the prior art to use so-called heat protection pastes in high temperature processes. With these pastes, however, the main function consists primarily in guaranteeing protection of the molded part to be treated thermally or its structural environment. These products, however, are intended for industrial use and are thus not suitable for use in the manufacture of dental products. Customary constituents of such pastes are glass fibers, glass powders, ceramic powders, and water and a thickening agent, such as, for example, various celluloses.
The disadvantage of these pastes consists especially in the fact that some ingredients of the pastes “adhere” to the molded parts and are intercalated into the surface of the molded part such that these residues of the pastes have to be removed mechanically. Removal can either be carried out by grinding or by sandblasting. Here, the great disadvantage in the removal of the paste residues is the mechanical surface damage of the restoration part, which can thereby lead to a reduction of the mechanical strengths.
Furthermore, it is known from DE 103 39 246 A1 to employ a heat protection paste which breaks down in the thermal treatment of a dental product made of materials having stresses resulting from different heat expansion coefficients to the extent that no stress cracks or even spalling occur. This heat protection paste consists of water, diethylene glycol, temperature-resistant fibers and suitable heat-resistant fillers. The heat-related warpage of the molded parts is not taken into consideration in this reference.
DE 198 53 949 A1 describes a sinterable ceramic composition for sintering together individual crowns and bridge segments to form a single strong dental restoration.
US 2003/0059742 A1 describes the use in dental implants of mineral nanofibers 0.1-100 nm in size. In this use, these nanofibers are sintered to form shaped articles, or implants composed of other materials become coated with these nanofibers. These sintered nanofibers are notable for good osteointegration.
Similar basic components to those in the present invention are described in EP 0 464 545 A2. However, such a composition would not work as a supporting paste since the formulation after the burning out of the organic paste exhibits excessive contraction in volume and there is no supporting effect.
DE 36 10 844 C2 discloses a further development of dental cements which set to form a strong cementaceous material having compressive strengths of >600 bar. It is desirable for cements that they possess good bonding to the components to be cemented.
DE 14 67 061 A1 discloses using starting materials such as zinc and iron. These can lead at high temperatures to reactions with the glassy or glass-ceramic moldings which, in turn, trigger color impairments or even chemical reactions which lead to surface disruptions and thus to strength losses.
From DE 198 53 949 A1, it is known for the connection of dental restoration parts to employ connecting members which are sintered by a glass powder paste. This paste or suspension serves here for the mechanically solid connection between restoration part and connecting member.
From the company Functional Designs, Inc. (USA), a supporting paste with the name Easy Fix is on the market, which is composed as follows:
water65-70%aluminum silicate fibers20-25%amorphous silicon dioxide 5-10%hydroxyethylcellulose  1-3%.
This paste fulfils the requirements with respect to the supporting function, but the fibers and the silicon dioxide adhere to the inside of the parts to be supported. The residues of the supporting paste remaining on the molded part must be removed using a particle blasting process (usually glass or glass ceramic powder). This process leads to damage to the surface structure and thus often to a decrease in strength of the entire molded part.
In the manufacture of dental restoration parts from only partly sintered zirconium dioxide, dense sintering is carried out at temperatures of about 1500° C. For this, it is likewise necessary to support this restoration part in the sintering process. For this purpose, various possibilities are known and in use.
Support can be carried out, for example, by intercalating the restoration part in a bed of thermally high-strength ceramic spheres or alternatively by “laying” the restoration part on pins which are arranged moveably and on shrinkage as a result of the sintering process compensates the shrinkage by inclining relative to one another. A further possibility, according to EP 0 817 597 B1, is to support the restoration part in a bed of the same partly sintered ceramic material which not only has a supportive effect, but at the same time has the same shrinkage as the restoration part.
A disadvantage in the previously known embodiments is that handling is complicated and that co-ordinated supporting systems have to be used for each application.